I also had this issue with my 65sj850v model. it is brand new 2017 model actually. I turned off Quickstart+(I am not sure the exact name of it), Delete unuse app.
Connect Lan instead Wi-Fi. All solution was not helpful.
My issue was only happened when I was using Web Browsing and watching movie clip. And I realize that it was happening only few specific web page made by Java. I thought this problem comes from that web page. since I am not using this webpage and not accessing. Problem is not happening again.